Number 1, koff~
First Pokemon generated was kakuna, so poison type.
I'll just use 1 Grimer and 2 Koffing since I'm the first gym.
Gym Type: Poison
Badge: Danger Badge
lvl-18 Koffing (M) Levitate
lvl-19 Koffing (F) Levitate
lvl-22 Grimer (M) Poisontouch
Before Battle: "Pokemon. They're all around us. Whether Pokemon are your friends or your enemies is up for you to decide; just don't forget about the ones you shun, they'll haunt you 'til your dying day"
After Battle: "I see. You seem to have the gumption to take your skills all the way. . . here, take these. *gives out selfdestruct TM and black sludge* That TM contains selfdestruct. It is a move of last resort; your pokemon will faint when they use it, but they'll often take others with them to the pokecenter. . . Black sludge heals the most despised pokemon, poison, and no others. Use them wisely. Don't ever forget who your friends are. . ."
How'd I do, koffi~